This invention relates to vehicles and in particular to a vehicle which has a cooling circuit including a thermostat.
It is a known problem that a thermostat in a vehicle cooling system can leak or become stuck in an open or closed position. It is desirable to monitor the operational efficiency of such thermostats because their failure can lead to reduced efficiency in some emissions related monitoring and control operations. For example, it is sometimes necessary for the coolant to reach a predetermined temperature before an on-board diagnostic operation can be carried out on a fuelling system or on an exhaust gas oxygen sensor. In one known case this temperature, (in the order of 80xc2x0 C.), may not be reached if the thermostat is stuck open or leaking. It is, therefore, desirable to detect such a faulty thermostat so that the fault can be indicated to a user or maintainer and the problem rectified.
The use of a test apparatus to check cooling system operation under workshop conditions is known, e.g. from U.S. Pat. No. 4,069,712, U.S. Pat. No. 4,702,620 and U.S. Pat. No. 5,526,871. The use of these known systems does not allow the vehicle itself to perform an on-board diagnostic routine to test thermostat efficiency.
One attempt to provide on-board diagnostic capability of thermostat operation is disclosed in FR 2773845, in which the actual temperature of the cooling water is compared with a calculated model of anticipated cooling water temperature.
It is an object of this invention to provide an improved vehicle.
Accordingly, the invention provides a vehicle comprising a cooling circuit including a thermostat arranged in use to control the flow of a coolant around at least a part of the cooling circuit, the vehicle further comprising a control means arranged in use to carry out an on-board fault detection test routine to establish the operational condition of the thermostat, the test routine being arranged to determine the condition of the thermostat from a comparison between a thermostat inlet temperature and a thermostat outlet temperature and to determine that the thermostat is faulty if the thermostat inlet temperature is below an opening temperature of the thermostat and there is a temperature differential between the thermostat inlet temperature and the thermostat outlet temperature which differential is below a predetermined fault threshold, the cooling circuit further comprising a radiator and the thermostat being arranged in use to control the flow of the coolant through the radiator, characterised in that the thermostat inlet temperature is derived from a top hose or radiator inlet temperature and/or the thermostat outlet temperature is derived from a bottom hose or radiator outlet temperature.
The test routine may be arranged to evaluate a said fault condition as a leaking or substantially stuck open thermostat.
The control means may be provided with a signal indicative of the thermostat outlet temperature from an outlet temperature sensing means positioned in the region of a bottom tank or outlet hose of the radiator.
The control means may be arranged to perform a diagnostic test on the outlet temperature sensing means and to test the condition of the thermostat only if there is no fault condition detected with said outlet temperature sensing means.
The control means may be provided with a signal indicative of the thermostat inlet temperature from an inlet temperature sensing means positioned in the region of a top tank or inlet hose of the radiator or positioned so as to sense engine block temperature or engine block coolant temperature.
The control means may be arranged to perform a diagnostic test on the inlet temperature sensing means and to test the condition of the thermostat only if there is no fault condition detected with said inlet temperature sensing means.
The control means may be arranged not to test the condition of the thermostat if the engine is running at an idle speed and may be arranged not to test the condition of the thermostat if the engine is operating in an over-run-fuel-cut-off mode. The control means may be arranged to test the condition of the thermostat only if the engine has been running for a predetermined period of time.
The control means may be arranged to record the detection of a fault with the thermostat, the fault condition being recorded in a retrievable manner which can be used so as to provide to a user or maintainer an indication that a fault with the thermostat has been recorded. Said indication may comprise the illumination of a malfunction indicator lamp (MIL) or an engine check light. The control means may be arranged to record a said fault with the thermostat only if said temperature differential remains present after a thermostat debounce delay.
The outlet temperature sensing means may be formed so as to act also as a drain plug for the radiator and the inlet temperature sensing means may comprise an engine temperature sensor.
Said fault threshold may be in the order of 30xc2x0 C.
The invention also provides a method of establishing the operational condition of a thermostat included in a cooling circuit of a vehicle by performing an on-board fault detection test routine which includes comparing a thermostat inlet temperature and a thermostat outlet temperature and determining that the thermostat is faulty if the thermostat inlet temperature is below an opening temperature of the thermostat and there is a temperature differential between the thermostat inlet temperature and the thermostat outlet temperature which differential is below a predetermined fault threshold, characterised in that the method includes deriving the thermostat inlet temperature from a top-hose or radiator inlet temperature and/or deriving the thermostat outlet temperature from a bottom hose or radiator outlet temperature.
The method may include evaluating a said fault condition as a leaking or substantially stuck open thermostat.